Graphene nanoribbons (GNRs) are basically long thin graphene strips. Due to their small dimensions and active electronic edge states, GNRs can exhibit finite (nonzero) band gap values, which can be tuned depending on their geometric features. Theory predicts and experiment confirms that the band gap in GNRs is inversely proportional to their width. Namely, GNRs may retain graphene's high carrier mobility while presenting a finite band gap.
These properties can make GNRs very valuable materials for the building of an assortment of nanodevices. GNRs can also be cross-linked or welded, i.e., joined, together to form a large-scale GNR network, which can be used as flexible, stretchable, and/or transparent electrodes for electronic and photonic devices.
Generally, compared with carbon nanotube (CNT) sheets, GNR networks may have higher transparency, lower resistance, and/or better adhesion with other materials.
To date, several methods have been developed for the synthesis of GNRs, including lithographical patterning of graphene, bottom-up organic synthesis, sonochemical cutting of exfoliated expandable graphite, chemical vapor deposition, oxygen plasma etching of graphene using nanowires as a physical protection mask, Li intercalation followed by exfoliation, and longitudinal unzipping of multi-walled CNTs.
Since CNTs are cylindrical shells that can be made, at least in concept, by rolling graphene sheets into a seamless cylinder, the unzipping of CNTs is a new and very promising approach for controlled and large-scale GNR production. In this process, CNTs are unzipped (opened or fractured) along their longitudinal axes in such a way that the obtained structures are the desired GNRs.
Unzipping CNTs has been practiced in many different ways using a variety of chemical and physical methods. However, these chemical and physical methods typically use strong acids, oxidizing agents, or other solvents. The wet-processes often alter the properties of GNRs for various reasons, including the high proportion of oxygen functionalities or particles that may contact the CNTs or GNRs. The alteration of the GNRs' properties can cause problems in device fabrication processes, because the alterations may lead to wrinkles and/or the folding of GNRs. The alterations may make it difficult to position the GNRs as desired.
Nevertheless, another advantage of using CNTs as starting materials to produce GNRs is the fact that the existing knowledge of CNT synthesis and purification methods can be used to control and/or optimize GNR fabrication.
Therefore, a way to produce GNRs from CNT starting materials that overcomes one or more of the difficulties associated with the known methods is desirable.